Brain abscess formation is a rare complication of intracranial endovascular treatment. To our knowledge, all previous reports of brain abscess formation have been associated with treatments involving the introduction of foreign materials. A 75-year-old man was admitted to hospital for acute stroke. Cerebral angiography revealed occlusion of the left middle cerebral artery (MCA) at the origin of the M2 segment. Intra-arterial thrombolytic therapy was administered but a hemorrhagic event occurred during this process. A brain CT scan revealed a hematoma extending from the left basal ganglia to the left frontal lobe and expansion of the infarct in the left MCA territory. A brain abscess at the hemorrhagic site developed 3 months after symptom onset. This is the first report of a patient with brain abscess formation following intra-arterial thrombolytic treatment. It is important to ensure aseptic technique during endovascular procedures irrespective of the involvement of foreign materials.